Potentiometric detection using a metallic copper electrode in reversed-phase and ion-exclusion chromatography with eluents containing ion-interaction reagents

The response characteristics of a metallic copper wire electrode used as a sensor electrode in a potentiometric detector after ion-interaction separations are determined. Volatile carboxylic acids have been selected as model compounds to test the sensor electrode. It is found that concentrations of an ion-interaction reagent (tetraethylammonium perchlorate) as small as 0.01 mM in an unbuffered mobile phase are optimal for the potentiometric detection and separation in two chromatographic systems, namely reversed-phase and ion-exclusion. The ion-interaction reagent gives improved solute peak shape and results in retention times becoming independent of solute concentration, without any adverse effect on detection sensitivity. An increase in the mobile phase concentration of the reagent results in increased solute retention in the ion-exclusion chromatography mode and variation of this concentration is a new parameter that can be used to control solute retention. Typical detection limits are 250, 510 and 360 pmol for acetic, propionic and butyric acids, respectively.